Current drill and blast advance rates are now at historic lows with only 4 m/day advancement possible with the most efficient and powerful equipment the mining industry has ever used. As little as 25 years ago, advance rates of 12 m/day or more were commonplace. Today, the safest and most efficient tunnel-advance technique is the tunnel-boring machine and is being developed for application to very large regular shaped ore-bodies, such as copper porphyries. Most underground base metal mines are too small and too irregular in shape to make use of this kind of technology.
The batch drill-and-blast technique has definite advantages in highly stressed grounds where seismic activity is prevalent. Blasting can be use to proactively initiate the seismic release of energy and the combination of pinned mesh coverage allows for surface expansion before rigid shotcrete support is added for long term stability.
The batch drill-and-blast process can be broken into three stages; removal of broken rock from the heading, face-advance activities, which include drilling holes and loading explosives, and ground support (i.e. roof and wall support) installation. Currently, the process of installing ground support is the most-time consuming component of the cycle and given the challenging safety and stability conditions encountered in deep mining, the quality of the final installation of this component cannot be compromised. In fact, in some cases protection from instabilities at the face may also have to be provided.
Two important characteristics of the tunnel-boring technique are (1) the reduction of exposure of the operating personnel from the danger of rock-related injuries in the heading, and (2) the simultaneous application of face-advance and ground support activities. Just as personnel are protected inside the tunnel boring machine, so must the batch drill-and-blast personnel be protected from exposure to rock-related risks at all times. To be more productive any new batch drill-and-blast process must emulate the simultaneous implementation of face-advance and ground support activities to increase the rate of advance.